The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to a carrier head for a chemical mechanical polishing apparatus.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, it is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d or a fixed-abrasive pad. A standard polishing pad has a durable roughened surface, whereas a fixed-abrasive pad has abrasive particles held in a contaimnent media. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent and abrasive particles, if a standard pad is used, is supplied to the surface of the polishing pad.
The effectiveness of a CMP process may be measured by its polishing rate and by the resulting finish (absence of small-scale roughness) and flatness (absence of large-scale topography) of the substrate surface. The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A recurring problem in CMP is the so-called xe2x80x9cedge-effect,xe2x80x9d i.e., the tendency of the edge of the substrate to be polished at a different rate than the center of the substrate. The edge effect typically results in over-polishing (the removal of too much material from the substrate) at the substrate perimeter, e.g., the outermost five to ten millimeters of a 200-mm wafer.
Another problem is that the polishing pad contacts and abrades the bottom surface of the retaining ring. Eventually, the bottom surface retaining ring will be sufficiently worn away that the retaining ring needs to be replaced.
In one aspect, the invention is directed to a retaining ring for a carrier head. The retaining ring has an inner core of a first material and an outer layer of a second, different material that is deposited on the first material.
Implementations of the retaining ring may include one or more of the following features. The outer layer may be deposited on the inner core by spraying. The outer layer may have a bottom surface for contacting a polishing pad during polishing. The second material may be less rigid than the first material. The second material may be a polymer, such as polyetheretherketone, and the first material may be a metal.
In another aspect, the invention is directed to a retaining ring for a carrier head. The retaining ring has an inner core made of a first material, and an outer layer of a second, different material that is configured to be replaced by redeposition.
Implementations of the retaining ring may include one or more of the following features. The outer layer may include a bottom surface for contacting a polishing pad during polishing.
In another aspect, the invention is directed to a method for assembling a retaining ring for a carrier head. The method includes providing an inner core of a first material, and depositing an outer layer of a second, different material onto an outer surface of the inner core.
Implementations of the retaining ring may include one or more of the following features. The outer layer may provide a bottom surface for contacting a polishing pad during polishing. The step of depositing may include spraying the second material onto the first material. The second material may be a polymer, such as polyetheretherketone. The deposition step may be a powder coating process or a dry finishing process.
In another aspect, the invention is directed to a method for repairing a retaining ring of a carrier head. The method includes providing a retaining ring having an inner core of a first material and an at least partially worn outer layer of a second, different material, and redepositing the second material of the outer layer on the retaining ring to refurbish the outer layer.
Implementations of the retaining ring may include one or more of the following features. The outer layer may provide a bottom surface for contacting a polishing pad during polishing. The redepositing step may include includes spraying the second material onto the retaining ring.